Clearwire CTO Sees 4G Specs Migration, Convergence as Workable

The two 4G standards share 75 percent of their DNA, as flat, OFDM-based and all-IP platforms, Saw said. So WiMAX facilities such as core networks, wide-area network and backhaul can be reused for LTE, he said. “Very little goes to waste” in switching from WiMAX to LTE, he said. The operator’s average holding of 120 MHz of 2.5 GHz spectrum in major markets allows a lot of flexibility for a possible transition, Saw said. The company could allocate some spectrum for WiMAX and later do an LTE overlay, using new spectrum in the same band, he said.

The operator has its eyes on both of the LTE standards for a potential migration. While most LTE operators (700 MHz spectrum holders) have adopted FDD-LTE (Frequency Division Duplexing) using paired spectrum with two separated channels, another LTE standard -- TDD-LTE (Time Division Duplexing) -- is gaining traction, Saw said. TDD-LTE uses unpaired spectrum channels that combine uplink and downlink, meaning it can operate in slimmer chunks of spectrum than its counterpart, he said, adding that there’s no major performance difference between the two. Clearwire, along with equipment vendors like Motorola, Nokia Siemens and Alcatel-Lucent, is asking the standards group 3GPP to expand the use of TDD-LTE by adding channels, Saw acknowledged. The company is also looking at ways to leverage FDD-LTE, Saw said: Clearwire is testing the use of FDD-LTE on its 2.5 GHz band.

Convergence is also possible, Saw said. “I don’t see a problem if you do the engineering right. We have spent a lot of time looking at that.” Clearwire is required under agreements with its investors to stay with WiMAX until November 2011, according to a 2009 SEC filing. But the agreements wouldn’t be a major stumbling block, Saw said. When the time is right to make any changes to the network, “we will sit down (with the investors) and make the best decision possible,” he said.

For now, the company is committed to WiMAX, Saw said. For the company to adopt a different standard, it must have a good ecosystem, reduce the cost of delivering service and trigger significant new devices and services, he said, emphasizing that no decision has been made. Meanwhile, Clearwire is interested in testing WiMAX 2, the 802.16m specification, as soon as it’s available, Saw said. “We are keeping our options open.” Any testing or field trials would be early next year, he said. The WiMAX Forum is pushing for WiMAX 2, an enhanced WiMAX standard expected to deliver peak rates of more than 300 Mbps (CD April 13 p6).

Clearwire isn’t slowing down its WiMAX rollout this year and deployment is on track, Saw said. Clearwire, with its wholesale partners Comcast, Time Warner Cable and Sprint announced their summer 2010 launch lineup Wednesday. Clearwire plans to add 18 markets before fall. Each operator will offer its own brand of WiMAX. Comcast will offer services in Merced, Modesto, Stockton and Visalia, Calif., Wilmington, Del., Grand Rapids, Mich., Eugene, Ore., Yakima and Tri-Cities, Wash. Time Warner Cable will offer WiMAX services in Kansas City, Kan., and Rochester and Syracuse, N.Y. Comcast will use the Comcast High Speed 2go brand in marketing WiMAX. It will be bundled with their home Internet connection in the markets. Time Warner will market the product under Road Runner Mobile. Clearwire and Sprint also plan to introduce WiMAX this year in markets including San Francisco, Los Angeles, Boston, Washington, Miami, New York and Pittsburgh, as part of Clearwire’s plan to cover 120 million people before 2011.